Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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Why isn't light scattered through transparency?

I'm asking a question that has bothered me for years and years. First of all, let me give some context. I'm a layman in physics (college educated, math major). I've read Feynman's QED cover to cover, ...
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4answers
6k views

What happens when a photon hits a mirror?

When a photon of light hits a mirror does the exact same photon of light bounce back or is it absorbed then one with the same properties emitted? If the same one is bounced back does it's velocity ...
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4answers
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Why does adding red light with blue light give purple light?

Our eyes contain 3 photoreceptor cells (cones) to perceive three wavelength ranges of light. Here is a visual representation of the wavelengths by these receptors (S, M and L). So if we have light ...
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2answers
747 views

Sun spectroscopy - Home experiment

We let the sun light run through a 5x3x3cm triangular glass prism and we examined the formed 'rainbow' in search of Fraunhofer lines. However, even though we looked close enough (even with a ...
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3answers
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Why do green lasers appear brighter and stronger than red and blue lasers?

This is mostly for my own personal illumination, and isn't directly related to any school or work projects. I just picked up a trio of laser pointers (red, green, and blue), and I notice that when I ...
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3answers
627 views

What gives things color? [duplicate]

I know that color comes from things not absorbing a certain wavelength of light, but what property gives something color? Like what property of copper atoms makes copper as a whole brown, or cobalt ...
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3answers
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What causes atoms to have their specific colors?

I understand that light (color) is part of the electromagnetic spectrum, and that it depends on what wavelengths are reflected/absorbed. Though what property of an individual atom gives it its color? ...
12
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1answer
462 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
12
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4answers
943 views

How does interference move energy from destructive to constructive regions?

I recently read (sorry but I don’t have a reference) that interference is not only about destructive and constructive interference but moving energy from destructive to constructive regions according ...
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6answers
556 views

How large is the universe?

We know that the age of the universe (or, at least the time since the Big Bang) is roughly 13.75 billion years. I have heard that the size of the universe is much larger than what we can see, in other ...
11
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1answer
525 views

Looking at an iPhone through a Polarizer

Maybe this is more of an Electrical Engineering question, but does anyone know why iPhones looking green/red through a linear polarizer? I find it strange that the light coming out would be ...
11
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4answers
426 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...
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4answers
515 views

Does the speed of medium affect the path of light?

Let's say I shine a laser from a stationary medium into a moving medium (suppose the water is moving very quickly) perpendicular to the interface and back to a stationary medium like this: (Note: ...
11
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2answers
358 views

What mechanisms allow conductors to be transparent?

An electric field in a conductor causes charges to redistribute so as to cancel out the original field, bringing the field to zero. This is, I think, a common argument for why conductors are generally ...
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5answers
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What happens to light and mass in the center of a black hole?

I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black ...
11
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1answer
733 views

Why Do My Fan Blades Produce Color When They Spin?

I've posted a short video here as a visual aid. Whenever I put my fan on Medium speed during the night time, it produces a rotating Blue and Orange color design, despite both fan blades being a white ...
11
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2answers
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EM wave function & photon wavefunction

According to this review Photon wave function. Iwo Bialynicki-Birula. Progress in Optics 36 V (1996), pp. 245-294. arXiv:quant-ph/0508202, a classical EM plane wavefunction is a wavefunction (in ...
11
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1answer
328 views

What causes the sharp borderline at the bottom of northern lights?

The northern lights are caused by cosmic charged particles interacting with the earth's upper atmoshphere. The particles can be trapped by the Lorentz force, so that we can see them where the magnetic ...
11
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1answer
265 views

Why do some sunsets have a green flash?

Some sunsets exhibit a phenomenon called "green flash," where there is a quick flash of green light right as the sun is setting. I have seen this myself several times, and sort of understand it. I am ...
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4answers
1k views

Why doesn't more light bounce off of things in the manner of sound?

If I'm sitting in the den with my door slightly cracked, I can hear my wife washing dishes in the kitchen down the hall. But why can't I also 'see' images of her washing dishes if, say, I looked up on ...
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3answers
15k views

What is the color of a mirror?

A mirror couldn't be white, as then you wouldn't be able to see your reflection so clearly. It wouldn't be transparent, as that then won't reflect. So what color is it?
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5answers
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Where does light go after it enters a black hole?

Nothing passes through a black hole. Where do things go then? If light enters a black hole, what happens to it? Do things go to a white hole and resume in another universe?
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3answers
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Why do stars flicker?

Why do stars flicker and planets don't? At least this is what I've read online and seen on the night sky. I've heard that it has to do something with the fact that stars emit light and planets reflect ...
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5answers
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What happens to light after it enters an eye

What happens to the light [energy] after it enters an eye and hits the rods and cones? I presume the energy becomes electrical, and it must be near 100% perfect, else our eyes would heat up? Or am I ...
10
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2answers
894 views

Why does the sky suddenly look gray through this window?

I am looking to the windowed roof of my building, and I notice that the sky, which has few white clouds, sometimes looks completely gray, as if there was a huge cover of gray clouds, but there are ...
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5answers
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Can someone explain the science behind MIT's 230% efficient LEDs?

I was reading Gizmodo the other day and I didn't quite understand the Physics behind this. Could anybody shed some light on how this effect actually works?
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3answers
763 views

Using a black hole as a mirror?

http://www.youtube.com/watch?v=ENd8Sz0AFOk The YouTube video is a good example how the gravity of this merging binary black holes bend light around themselves.
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1answer
51 views

Glowing light around my shadow during sunrise

This morning I was jogging when the sun came rose. I was in the middle of wheat-fields and noticed that there was a glow around the upper part of body's shadow on the fields. At first I thought that ...
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3answers
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Conservation of energy and Doppler effect?

From what I understand, the frequency of light coming from the source moving towards an observer increases. From $ E=hv $ , this implies increase in energy of photon. What really is confusing, is ...
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6answers
4k views

Why is Light invisible?

Why can't we see light? The thing which makes everything visible is itself invisible. Why is it so?
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2answers
1k views

If light rays obey to the wave equation, why can they be thought as straight lines?

I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object ...
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4answers
9k views

Can someone explain the color Pink to me?

I just finished watching this interesting video: http://youtu.be/S9dqJRyk0YM It does a very quick explanation of how pink light doesn't exist, and that the concept of pink is our brain's attempt at ...
9
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4answers
2k views

How many percent of the visible light reaching the Earth are from other stars than the Sun?

How many percent of the whole visible light reaching the Earth are from other stars than the Sun? Is it maybe 0,5 - 1% or is my guess already too much? I am interested mainly in visible light, but ...
9
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2answers
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Is it possible to charge photons

For example there are anti-particles to every particle we know, Similary in some sense, is there a possibility that we can charge photons..if not what are the reasons and has there been any attempt ...
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3answers
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Is there a light source that emits all wavelengths of visible light at the same time?

Many light sources like LEDs and lasers only emit a single wavelength of light. Is there a light source that emits all wavelengths of visible light at the same time?
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4answers
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Why is the speed-of-light “the upper limit” rather than the speed of “particle type X”?

Basically, I can't stop wondering why light (the photon) is so special, compared to all the other particles known (and unknown) to modern day physics. Could it be that there exists an upper limit on ...
9
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2answers
1k views

Would using Cherenkov radiation for lighting be feasible?

Could Cherenkov radiation be used for general illumination, for example, to replace LEDs, light bulbs etc? I.e. are there, or could there be, methods to produce substantial amount visible light with ...
9
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1answer
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Distribution of star colours in a galaxy

I'm trying to randomly generate a representation of a galaxy. I have some Idea on the spatial distribution of stars within a galaxy, and I can find plenty of material on the colour of stars, but ...
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2answers
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Squinting at street lights

Simple question, I've always wanted to know the answer to this. Why do you see a pair of lines radiating out from street lights when your squint at them? I can't think of a better way of describing ...
9
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2answers
302 views

Which of these theories on why light slows in media are true?

This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity. It's a ...
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5answers
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Superposition of electromagnetic waves

The superposition of two waves is given by $$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$ For sound waves, this ...
9
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2answers
88 views

Why is reflected light polarised?

Why is reflected light polarised? I have learnt about Brewster's angle, and how at a particular angle all light reflected is polarised, but do not understand why. Is this something that could be ...
9
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5answers
763 views

Will freely rotatable polarizers align?

Will two freely rotatable linear polarizers (placed in sequence and at some angular offset less than, say, 45 degrees) eventually align if you shine (plenty of) unpolarized light at the first one? If ...
9
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6answers
32k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
9
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1answer
463 views

How fat is Feynman’s photon?

According to my calculations, it is a lot skinnier than Airy’s photon, but still a whole lot fatter than a straight line. So, how does a photon get from point A to Point B? The ray optics ...
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4answers
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What makes some laser beams visible and other laser beams invisible?

What makes the beam of some lasers: visible? such as the ones used in clubs or such as the laser pointers sold at amazon which if pointed to the sky look like a solid visible beam of light ...
8
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3answers
200 views

Why doesn't $ds^2 = 0$ imply two distinct points $p$ and $p'$ on a manifold are the same point?

Let's suppose I have a spacetime manifold $M$. Let $p$ be a point on my manifold. Now I move from $p$ to some other point $p'$. Presumably I should have moved some "distance" right? How can I speak of ...
8
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4answers
442 views

How can a body be transparent?

How can a body be transparent? I need the theoretical explanation for the same. Has anybody succeeded in doing that practically?
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2answers
636 views

Are there “gaps” in light, or will it hit everywhere?

Not sure how to word my question. Picture a light source in vacuum, so nothing disturbs the light (or similar conditions), 2d. If I move very, very far away, will it happen that some of the light ...
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5answers
3k views

Why can't we see infrared light?

While explaining to my nephew about the physics of light, I told him we cannot see infrared color, and he kicked back with a very simple question: why can't we see it? I could not tell him. Is the ...